CT technology has been playing an important role in occasions such as security inspection, thanks to its capability of eliminating influence from object overlapping. Conventional CT apparatuses use a slip ring device, and acquire projection data at different angles by rotating X-ray source and detectors. Then, the CT apparatuses reconstruct a tomogram image to obtain information of the inside of the inspected luggage or articles. In combination with dual-energy or multi-energy imaging technology, the existing inspection apparatuses can reconstruct atomic number and electron density of the inspected object, and identify materials contained in article, achieving good effects in detecting explosives or drugs, for example.
The existing CT technology for security inspection has disadvantages. First, there is a problem with the scanning speed. A high speed is helpful to mitigation of pressure caused by a large number of passengers and cargoes. However, a high-speed scanning typically requires a slip ring that can rotate at a high speed. Due to difficulties in fabrication precision and reliability, for example, the high-speed slip ring is very expensive in manufacture and maintenance, and thus is difficult in popularization. Second, there exist problems such as false alarm and missing alarm. It is difficult for the automatic identification and alarm functions in the CT technology to achieve an accuracy of 100%, and thus detection of contraband still requires manual auxiliary examination, and sometimes it even requires opening a luggage case for examination. Such examination often takes several or tens of minutes, which increases labor and time cost and limits improvement in examination efficiency. In order to address these problems, an apparatus using secondary scanning technology has been introduced into market, which can reduce a frequency of opening the luggage case by performing a high-accuracy secondary scanning on any suspicious luggage case to improve CT image quality. This secondary scanning, however, also results in increased scanning time and interruption in the security inspection process.
In recent years, the technology of carbon-nanotube X-ray tube has been introduced to practical applications. Unlike normal X-ray sources, the carbon-nanotube X-ray tube does not require high temperature for generating rays. Instead, it generates cathode rays based on principle of discharging of carbon-nanotube tip, and uses the cathode rays to strike a target to generate X rays. Such X-ray source has advantages of rapid switch-on/off, and a smaller volume. A “static CT” apparatus without rotation can be formed by arranging the X-ray source properly and irradiating X-rays onto the object from different directions. This significantly accelerates the radiography process while omitting the slip-ring structure and saving cost, thereby contributing a lot to the field of security inspection.